Resistance to five ACCase-inhibiting herbicides (dictofop, fluazifop, tralkoxydim, cycloxydim and pinoxaden) was investigated in 55 Lolium multiflorum populations from 50 farms in England. Resistance screening experiments at whole plant level showed differences in the response to each herbicide suggesting different resistance mechanisms for different herbicides, despite all of them having the same mode of action. Plants from populations resistant to at least one herbicide were analysed at the molecular level using the derived Cleaved Amplified Polymorphic Sequence method (dCAPS). Three single-site point mutations (ile-1781-leu, asp-2078-gly and cys-2088-arg) known to confer resistance to ACCase inhibitors were found in 13 populations. In the remaining resistant populations a more specific mutation or an enhanced metabolism mechanism might be involved.